For UK based charities there is an organisation called CT Exchange - see http://www.ctxchange.org who themselves are a charity. They provide hardware & software, including most of the Microsoft suite of products for a small admin fee - for example a copy of Microsoft Office Professional would cost £10+VAT. And if you are slightly larger then something like Microsoft Small Business Server for £35+VAT is an excellent product for running a network.
If you are after hardware then Cisco provide cheap (but top quality) kit for drastically reduced prices through the scheme.
We came across it as a charity wanted to purchase licenses for Microsoft Office Sharepoint Server and it was a very cost effective way of them getting the licenses.
There are some eligibility criteria (e.g. you have to be registered with the charity commission) and there are limitations on how many licenses you can order but it might be worth checking out. More info at http://www.ctxchange.org